<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
.header{
    margin: 0 auto;
    max-width:960px;
    height:100px;
    background:blue;
}
nav{
    margin:0 auto;
    max-width:800px;
    background:blueviolet;
    height:50px;
}
.content{
    margin:0 auto;
    max-width:800px;
    height:400px;
    background:plum;
}
.footer{
    margin:0 auto;
    max-width:960px;
    height:100px;
    background:pink;
}
</style>
<body>
    <div class="header">
        <nav></nav>
    </div>
    <div class="content"></div>
    <div class="footer"></div>
</body>
</html>